Imagine you're swimming in a massive, crowded,
underwater neighborhood. But this is definitely
not a vibrant little coral reef filled with colorful
fish darting around anemones. Right, no. You
are swimming through a Jurassic Sea. And every
single shadow passing over you belongs to an
apex predator. It's a prehistoric ecosystem packed
to the absolute brim, just overflowing with marine
reptiles, heavily armored fish, and these deep
diving ichthyosaurs. It's terrifying to even
picture. And today we are going to focus on one
very particular creature from this ancient ocean,
a creature that, well, scientists have been arguing
about for over 150 years. Yeah, it genuinely
stands as one of the most frustrating and honestly
fascinating taxonomic puzzles in all of paleontology.
Because the animal we're examining today has
been named, renamed, categorized, and then aggressively
evicted from its own family tree more times than
almost any other marine reptile. It really is
the perfect case study. It shows exactly how
difficult it is to categorize ancient life when
all you have are scattered fragments of bone
and a constantly shifting understanding of evolution.
Which brings us to today's source material. We're
pulling from a comprehensive Wikipedia article
detailing the extinct marine reptile currently
known as Pleiosaurus andrusi. Or at least that's
what we call it for now. Right. So our mission
for this deep dive is threefold. First, we're
going to explore the century and a half long
soap opera of how this animal was actually classified.
The drama is real with this one. It really is.
Second, we're going to reconstruct this unique
apex predator from snout to flipper, looking
at a physical contradiction that completely baffled
scientists. A very weird contradiction, yes.
And third, we are going to figure out exactly
how it managed to survive in a sea completely
overloaded with rival sea monsters. Okay, let's
unpack this. Starting with an identity crisis
that spans generations of paleontologists. Calling
it an identity crisis might actually be underselling
it. The timeline of discovering and naming this
animal is incredibly convoluted. Let's wind the
clock all the way back to 1871. We have a scientist
named John Phillips. Right, and he's examining
some plasaur fossils that were found by Charles
Leeds over in England. Specifically in the Oxford
Clay Formation, yeah. So Phillips is looking
at a swimming paddle. And a pretty well -preserved
jawbone. And he analyzes these pieces and he
decides to name the creature Pleiosaurus, question
mark, Grandus. He literally includes a question
mark in the official scientific name. He does.
I mean, that feels like the 19th century equivalent
of a paleontologist just throwing their hands
up in the air and saying, I have no idea. It
really is. But it's also a remarkable bit of
honesty for that era. Because that question mark
tells you immediately that Felix wasn't entirely
convinced by his own classification. He knew
he had a large marine reptile, but the proportions
just didn't fit, right? Exactly. The morphology
of that jawbone didn't neatly align with the
existing understanding of the Pleiosaurus genus
at the time. And that initial hesitation, well,
it basically opened the floodgates for decades
of taxonomic chaos. Total chaos. Because jump
to 1889 and another paleontologist, Richard Lidecker,
steps up to the plate. Lidecker takes one look
at the specimen and decides Phillips was completely
wrong. Right. He moves the animal into a totally
different genus. He renames it Planastes phylarchus.
But he doesn't even stick to his own theory.
No, he doesn't. Just one year later in 1890,
he changes his mind again. Just because he notices
these bones are significantly larger than other
typical Pleinastes specimens. Right, so he reassigns
it yet again to a proposed species called Pleinastes
avansi. This sounds exhausting. A classic problem
in early paleontology, honestly. Size was very
often used as a primary metric for determining
a new species. Instead of looking at the actual
nuanced anatomical differences. Exactly. Lidecker
saw a bigger bone and just assumed, well, it
has to be a different species within the Polonistes
umbrella. And so the animal just sat there, categorized
under that name, gathering dust until 1913. Which
is when Charles William Andrews enters the narrative.
Right. Andrews examines a partial skeleton of
a large pliosaur found by Leeds, and he starts
to notice fundamental structural differences.
He realizes that the jaw and the vertebrae are
morphologically completely distinct from Polonistes.
He essentially looks at it and says, this isn't
Pellenestes and it isn't quite Pliosaurus. It's
doing its own thing. He recognizes it as an intermediate
form, a bridge between species. But amazingly,
it takes almost another 50 years for anyone to
formally act on Andrew's observation. Science
can move. Very slowly sometimes. Yeah. Fast forward
to 1960. A scientist named Lambert Beverly Tarlow
decides to finally clean up the mess. Tarlow
selects a very specific partial skeleton, one
that features a complete spine, the jaw, and
the limbs. And he designates that as the holotype,
the gold standard for the species. Right. And
he officially names the creature Pleiosaurus
andrugosae. He uses that specific epithet to
directly honor Charles William Andrews for his
insights way back in 1913. And at that point,
you would think the debate was finally closed,
right? You really would. Tarlow established a
holotype, honored the scientist who recognized
its unique traits, and firmly planted it in the
pliosaurus genus. For decades, this classification
was considered entirely settled. But taxonomy
is never truly finished. No, it simply waits
for better analytical tools. Which brings us
to the 2010s. when modern science drops a massive
plot twist on this poor creature's identity.
After fighting for a century to get this animal
properly classified into the Pleiosaurus genus,
a new wave of researchers ended up kicking it
right back out. They did. What's fascinating
here is how the advent of modern computational
biology completely upended a century of visual
assumptions. What's fascinating here is exactly
that. In the early 2010s, Researchers conducted
rigorous phylogenetic and anatomical revisions.
They took all the morphological data, every ridge
on the teeth, every measurement of the vertebrae,
the exact proportions of the skull, and fed it
into modern cladistic analyses. So they let the
computers do the heavy lifting. Right. And the
resulting family tree was undeniable. This animal
possessed unique characteristics, particularly
in its teeth, that separated it from every valid
species of Pliosaurus. It's incredible. The computer
essentially looked at the data and confirmed
what John Phillips suspected in 1871 with his
little question mark. Full circle. Yeah. And
because it doesn't belong in Pliosaurus, but
hasn't officially been assigned a new genus name
yet, the scientific community handles this in
a wonderfully quirky way. Today, its name is
written as Pleiosaurus in quotation marks, followed
by Andrusi. It wears those quotation marks like
a temporary badge, just signifying its pending
taxonomic status. It's like calling it the artist
formerly known as Pleiosaurus. So where does
it actually belong? Well, the current consensus
places Pleiosaurus Andrusi as a basal member
of a clade called Thalassophonia. Okay, let's
break that down for the listeners. Sure. Phallosophonia
is a specific group of short -necked pliosaurs.
And being a basal member means it sits near the
root of that family tree. It's somewhere right
between Poliniastes and Simulastes. So it's a
transitional form. Exactly. Being a transitional
form like this makes its anatomy incredibly revealing
because it bridges the evolutionary gap between
completely different types of specialized marine
hunters. Let's actually build this beast for
you, the listener, because the anatomy is where
this story shifts from a historical puzzle into
a true biological marvel. Paint the picture.
If this animal swam past you in that Jurassic
Sea, it would present a classic pleosauromorph
body plan. It was a medium -sized marine reptile.
But keep in mind, medium in this ecosystem means
it had a skull that measured one full meter in
length. It's over three feet of pure jaw and
muscle, just the head. Right. Behind that massive
skull, it had a heavily built barrel -shaped
body. Which was designed for powerful bursts
of speed rather than sustained graceful cruising.
And it had a remarkably short neck, like exactly
78 .3 centimeters long, based on a 2023 study
of the Holotech specimen. They get incredibly
precise with these measurements. And to navigate
the water, it utilized four large flippers. But
the back pair were larger, right? Yeah, the hind
flippers were noticeably larger and more robust
than the front ones, which provided the primary
thrust for swimming. But the defining feature
of this animal, the thing that caused so much
confusion, is what was going on inside that one
meter skull. The teeth. At the very front of
the jaw were the two halves, meet the symphysis
it had up to 12 pairs of teeth. And the seventh
pair were these massive, deeply rooted, canine
-like teeth. Operating with about 64 teeth in
total. And the structure of those teeth is the
absolute key to unlocking its ecological role.
They are highly distinct. In cross -section,
they're completely round. and they feature these
subtle longitudinal ridges running down the crown.
But that's not the weirdest part. No. The critical
detail of the anomaly that separates it from
its close relatives is the wear and tear. The
dental crowns exhibit a level of extreme abrasion.
It extends considerably further down the tooth
than in any other known plesiosaur. This is the
grand contradiction of Pleisosaurus and Druzy.
If you look at the shape of its skull, it has
an elongated, narrow snout. Which, evolutionarily
speaking, is almost universally adapted for catching
small, agile, slippery fish. Right. A narrow
snout lets a predator snap its jaws shut through
the water quickly because there's minimal drag.
But its teeth tell a totally different story.
Exactly. Its teeth were perfectly suited for
heavy -duty cutting, and they were heavily worn
down. If we connect this to the bigger picture
for a second, you do not get extreme dental abrasion
and deep wear patterns on cutting teeth from
eating soft -bodied fish. You just don't. That
specific type of wear strongly indicates it was
attacking much larger, highly resistant prey.
It's an incredible morphological paradox. It
possessed the quick -snapping, low -drag jaw
of a fish eater combined with the heavy -duty,
heavily -worn dentition of an apex big game hunter.
It completely broke the standard ecological rules
regarding what long -snouted predators are actually
supposed to hunt. So to understand why it evolved
this specific contradiction, we need to look
at exactly where it lived. We are traveling back
to the Kolovian stage of the Middle Jurassic.
Spanning roughly 166 to 164 million years ago.
Geographically, we are focusing on the Peterborough
member of the Oxford Clay Formation in modern
-day England. Though the geography of the Calovian
stage was vastly different from today. Right,
the landmass that would eventually become England
was submerged beneath an epicontinental sea.
A shallow inland sea, situated at a latitude
of roughly 35 degrees north. And when we say
shallow, we really mean it. A depth of only about
30 to 50 meters. That's incredibly shallow for
a sea packed with giant monsters. It is. But
up in the surrounding land masses, the environment
was surprisingly pleasant. It featured a Mediterranean
climate with dry summers and wet winters. Though
the region was gradually shifting toward a more
arid climate. But the water itself was temperate.
Isotope analysis from fossilized bivalves shows
that the water temperature averaged around 15
degrees Celsius. Or 59 degrees Fahrenheit. Right.
And it fluctuated seasonally, dropping to about
11 degrees Celsius in the winter and warming
up to 17 degrees in the summer. But the chemical
composition of that 50 meter deep water column
was highly unusual. The sediment reveals the
presence of green sulfur bacteria. And what does
that tell us? Well, in modern marine environments,
Green sulfur bacteria are a clear indicator of
eucinic conditions. Meaning low oxygen. Severely
depleted oxygen levels, yes. Paired with high
concentrations of toxic hydrogen sulfide. Typically,
those chemical markers suggest a stagnant dead
zone where complex life just cannot survive.
But the Peterborough member was the furthest
thing from a dead zone. The fossil record is
packed with abundant traces of benthic organisms,
creatures thriving right down on the seafloor.
Which tells us that while there were definitely
eucenic elements to the water chemistry, the
bottom waters were not completely or permanently
anoxic. The oxygen levels were dynamic. Here's
where it gets really interesting. Because the
sheer volume and diversity of life sharing this
specific body of water is just staggering. Oh,
it was packed. If you were diving in this 50
meter deep epicontinental sea, you... You'd be
surrounded by vast swarms of invertebrates, shelled
ammonites, belemnites. You'd see a massive variety
of fish, too, ranging from small, agile swimmers
all the way up to lead sickness. Right, that
colossal, filter -feeding fish that cruise through
the water like a Jurassic baleen whale. You would
also encounter smaller, long -necked plesiosaurs
like Cryptoclytus, specializing in darting its
head around to snatch up small prey. And don't
forget Ophthalmosaurus, that highly specialized
ichthyosaur with a porcus -like... body and gigantic
eyes, perfectly adapted for diving into the darker
depths to hunt squid. Add to that multiple genera
of marine crocodilians, some sleek and adapted
for fish catching, others heavily armored. But
the invertebrates, the giant fish, the marine
crocs, they weren't the real issue in this ecosystem.
The primary overcrowding problem came from the
pliosaurids. The apex predators. Right. The fossil
assemblage at the Peterborough member contains
more species of pliosaurids than any other known
site on Earth. This raises an important question.
How do you fit that many distinct apex predators
into a single shallow inland sea without them
completely devastating the food web or just fiercely
out -competing each other into extinction? Let's
look at the... absolute gauntlet of neighbors
that our animal, Pliosaurus and Drusae, had to
deal with. You have Leopleurodon, Similostes,
Poloniestes, Marmonectes, Vertosaurus, and Pachycostosaurus.
That is at least seven different massive, heavily
armed, carnivorous marine reptiles occupying
the exact same 50 meters of water. It sounds
like a recipe for starvation. How did they do
it? The mechanism that allowed them to coexist?
is a biological concept known as niche partitioning.
Meaning they divided up the resources. Exactly.
In highly crowded ecosystems, evolutionary pressure
forces predators to specialize incredibly thoroughly.
They divide the available resources so precisely
that direct competition is minimized. They essentially
split up the buffet menu. That's a great way
to put it. And the Peterborough member stands
as a master class in how nature engineers this
delicate balance. Let's walk through that divided
buffet. First, you have Liopleurodon and Erdosaurus.
Right. These were the absolute heavy hitters
of the ecosystem. They possessed massive, structurally
robust skulls and powerful cutting teeth. So
they claimed the top of the food chain. They
did. They specialized in hunting the largest
prey available, which likely meant preying on
other large marine reptiles and the biggest fish.
Then you have semolestes, which took a completely
different morphological approach. It featured
a very wide, exceptionally deep skull that housed
a tremendously powerful bite force. Its specific
niche was likely crushing large, tough -shelled
cephalopods. It didn't need a streamlined snout
to chase fast fish. It simply needed the raw
mechanical jaw strength to shatter heavy armor.
On the opposite end of the spectrum, you have
the fast fish hunters. That nooch was dominated
by palenonastes. Right. It evolved a highly elongated
snout and sharp, piercing teeth, making it perfectly
adapted for snapping up small, highly agile prey
with minimal water resistance. We also have to
mention Pachycustasaurus, which found an entirely
different way to avoid competition. It was a
smaller, exceptionally heavily built pliosaur.
Its skeletal structure was incredibly dense,
and its skull was structurally weaker than the
midwater hunters. So it stayed low. Exactly.
That immense bone density made it highly stable,
strongly suggesting it was a dedicated bottom
feeder. It cruised along the seafloor, picking
up benthic prey, keeping completely out of the
way of the massive predators hunting above it.
Which brings us back to Pliosaurus indrusi navigating
this incredibly specific ecosystem with its cortation
marks and its contradictory anatomy. Right, because
it was physically larger than the fish -eating
Polonastes, and it shared that same low -drag,
elongated snout. But it also possessed those
uniquely worn -down, heavily abraded, cutting
teeth. Through niche partitioning, Pliosaurus
and Druzy carved out its own highly specific
menu item. It utilized its quick -snapping jaws
to capture prey that was larger and tougher than
the other long -snatted predators could handle,
relying on its specialized cutting teeth to slice
through them. Every single one of these massive
marine reptiles survived by becoming a hyperspecialist.
They subtly treat the length of their snouts,
the exact cross -section of their teeth, and
the density of their skeletal structure, just
enough to claim a unique, undisputed slice of
the ecosystem. It is a stunning demonstration
of evolutionary adaptation thriving within a
confined environment. It really is. So what does
this all mean? We started this deep dive looking
at a confusing collection of bones that had paleontologists
second -guessing themselves from 1871 well into
the 2010s. And we uncover two brilliant takeaways.
First, we see that science is a living, continuously
self -correcting process. The quotation marks
around Pliosaurus aren't a failure of taxonomy.
They're a testament to the rigorous, ongoing
revision of our understanding as new data and
cladistic tools emerge. Absolutely. And second,
we wit - the sheer brilliance of niche partitioning.
Life in the Oxford Clay Formation didn't just
fiercely compete for a single resource. It adapted,
partitioned, and specialized, allowing an incredibly
diverse community of apex predators to thrive
together in a shallow, fluctuating sea. There
is, however, an inevitable consequence to that
level of brilliant specialization. What do you
mean? Well, the fossil record reveals that these
long -snouted, passivorous forms like Pliosaurus
and Drusii completely died out at the boundary
between the middle and upper Jurassic. Oh, wow.
Yeah. This specific extinction event kicked off
a gradual widespread decline in all plesiosaur
diversity. And it wasn't caused by a sudden catastrophic
asteroid impact. It was driven by shifting ocean
chemistry and steadily falling sea levels. So
the environment just slowly changed around them.
Exactly. An ecosystem becomes as perfectly partitioned
and tightly specialized as the Oxford Clay Sea,
where every animal has evolved a highly specific
jaw to consume a highly specific prey item. That
very perfection makes them incredibly fragile.
Because they have no backup plan. Right. When
the ocean chemistry shifts and the water levels
drop, the available buffet menu changes. Teeth,
your jaw, and your entire body plan are irreversibly
designed to eat only one thing. You are left
entirely without options when that one thing
disappears. That is a fascinating and sobering
thought to leave on. Thank you for joining us
on this deep dive into the chaotic taxonomic
history, the bizarre anatomy, and the densely
packed world of Pliosaurus and Drusorsi. Keep
digging into the mysteries of the ancient world,
and we will catch you on the next one.